Materials to be embedded in living bodies (i.e., implant materials) include metals, bioceramics, polymers, those with biological origins and hybrid materials.
These materials may be classified into so-called absorbable ones which are gradually absorbed and discharged from the body after exerting the functions in vivo and non-absorbable ones which cannot be degraded but substantially remain as such in vivo.
When these non-absorbable materials (synthetic materials) are kept in vivo over a long time, it is feared that these foreign matters undergoes some undesirable reactions due to the differences in physical or chemical (physiological) properties from biological constituents or the expression of toxicity caused by corrosion. Therefore, these materials are sometimes taken out from the body, if possible, by reoperative surgery. In such a case, a patient should be burdened with repeated pains and an additional fee. To relieve this situation, it has been required to develop biological materials which can be used as substitutes for the existing ones without resorting to any reoperative surgery.
Although biodegradable and absorbable materials are expected as useful in satisfying the above requirement, there are not such a great variety of absorbable materials as being usable as substitutes for all of nonabsorbable implant materials made of metals, ceramics, polymers, etc. Thus, research and development have been made to obtain a substitute for each of these existing materials.
Operative suture yarns and metallic materials (stainless steel, titanium, silver, platinum) employed for ligating missing or amputated parts are biomaterials which remain in the body after the completion of the operation. Suture yarns should be selected by considering tissue disorder, tissue tension, the occurrence of suture complication, effects of bodily fluids on the threads, infection, etc.
In general, silk yarns are employed in ligating fasciae and peritonea, nylon yarns are employed in ligating skin and nerves, polyester yarns are employed in fixing heart and tendons, while polypropylene yarns are employed in anastomosing nerves and blood vessels. Synthetic absorbable suture yarns (polyglycolic acid-based type) are used not only in the above sites but also in digestive tracts, etc.
In sites where a high strength is needed, on the other hand, use is made of metal wires made of stainless steel, titanium, etc. However, use of these metallic materials brings about troubles in image diagnosis. That is to say, light reflected thereby causes halation in magnetic resonance images (MRI) or computer tomography (CT) which have been rapidly spread in recent years as means for monitoring the conditions of patients under operation or postoperative healing state. Thus, it has been required to develop novel materials for suture, anastomosis or ligation which are usable as substitutes for metal wires.
As described above, various suture yarns are selected in operations to suit the occasion. In many cases, these yarns are employed in stanching, suturing or anastomosing various sites other than the main incised part. However, it sometimes takes the greater part of time to perform these treatments. Under these circumstances, it has been required to develop materials for suturing, anastomosing and ligating with which these treatments can be carried out more easily.
For example,. an incised tendon is fixed by suturing with a yarn. However, the procedure therefor has been becoming more and more complicated and it is therefore needed to develop fixation materials and convenient methods therefor. In operations in the thoracic or abdominal cavity, it is frequently observed that more than 50 blood vessels are incised. In such a case, it is necessary to perform suture and ligation at least 100 times for stanching and postoperative fixation. Therefore, it has been required to develop methods and materials by which these procedures can be carried out more easily. In addition, it is a practice to leave the conventional nonabsorbable materials as such in the body, since bypasses can be spontaneously formed after ligating blood vessels. Further, it is troublesome and risky to open-out the body again to take out metal clips, staples or various suture yarns therefrom, and there arises a dilemma that the body once opened-out should be sutured again. Accordingly, it is ideal that the materials to be used for the above purposes are biomaterials which can be degraded and absorbed in vivo and then discharged from the body, since the above-mentioned problems can be avoided by using these materials.
To achieve the above object, attempts have been made to produce staples and clips made of biodegradable and absorbable polymers (polyglycolic acid, polylactic acid, glycolic acid/lactic acid copolymer, polydioxanone, etc.) which have been molded into particular shapes designed by taking the physical strength of the polymers into consideration and can be physically caulked by using particular instruments. These products are used in operations in practice. However, these products still suffer from some disadvantages. Namely, they are troublesome in handling. In addition, they should be considerably larger in size than metallic ones because of the poor physical strength thereof. Moreover, they cannot be fastened tightly, since they are inferior in ductility to metals.